It is well recognized that the appropriate dose for many medications is related to a number of variables, including, for example, the size, weight, and/or physiologic state of the patient being treated. This variation is readily apparent from the different recommended doses many medications have for adults and children. The appropriate dose of contrast media for a given medical imaging procedure also tends to be dependent upon the size and weight of the patient being examined as well as additional factors.
Although differences in dosing requirements for medical imaging procedures have been recognized, many conventional medical imaging procedures, including angiographic, computed tomography, magnetic resonance and ultrasound imaging, continue to use pre-set doses or standard delivery protocols for injecting contrast media for medical imaging procedures. Although using fixed protocols for delivery simplifies the procedure, providing the same amount of contrast media to patients of varying size and weight can produce very different results in image contrast and quality.
It is typically desirable to coordinate the time of the image acquisition with the time of greatest levels of contrast in the region of interest, in some instances, with respect to a threshold value. Many physiological factors can affect the start time and duration of a sufficient level of contrast in the region of interest. For example, because the cardiovascular system generally provides the means for circulation of contrast agent throughout the body after it is injected, a patient's cardiac output can have a significant effect on the distribution of the contrast agent as well as the time taken for the contrast agent to reach a particular organ or vessel.
Current understanding of intravenous contrast enhancement is further complicated by multiple interacting factors. As such, in many respects, contrast enhancement still relies heavily on the experience and intuition of the physician rather than rigorous, quantitative analysis of the mechanism of contrast enhancement.